Heretofore, it has been performed to display drawings on a monitor display on the basis of graphic data prepared in advance by a computer and stored in a storage unit, and to correct (delete, add, and the like) the displayed graphics. (This is referred to as computer mapping hereinafter). Such drawings include ones showing the condition of underground facilities such as gas pipes, water pipes, and the like, and ones showing configurations of roads and conditions of road facilities.
FIG. 18 shows an arrangement of a conventional computer mapping system.
This system comprises a host 21 and a terminal 29, which are interconnected by a communication line 37.
The terminal 29 comprises a communication interface 30, a control processor 31, a picture memory 32, a frame buffer 33, a CRT ( display portion) 34, a digitizer (input portion) 35, and an image bus 36.
The host 21 comprises a memory 22, a communication interface 25, a host processor 26, a common file storage unit 27, and a host bus 28.
The memory 22 has an application program storing area 24 for storing application programs, and a work area 23.
Graphic data stored in the common file storage unit 27 has a format, for example, as shown in FIG. 19. It comprises a header 51, and graphic data 52 following the header 51. The graphic data 52 comprises coordinate data 53 indicating positions of characteristic points (or inflection points) of lines, and attribute data 54 indicating line types, colors, and the like between a characteristic point and the next characteristic point. Hereinafter, a set of the coordinate data and the attribute data is referred to as characteristic point data (or inflection point data).
FIG. 20 is a flowchart showing an application program stored in the application program storing area 24.
Suppose that a drawing (paper) to be edited is set on the digitizer 35. In this condition, when a display request command is issued in step S201 by operator's handling of the digitizer 35, and a drawing number specifying the drawing to be edited is entered, the display request command and the drawing number are transferred to the communication interface 30 through the image bus 36 by the control processor 31, and then transmitted to the host 21 through the communication line 37 by the communication interface 30 in step S202.
When the display request command and the drawing number are received by the communication interface 25 of the host 21 in step S203, the graphic data set of the drawing to be edited associated with the drawing number is retrieved from the common file storage unit 27 by the host processor 26. The retrieved graphic data set is stored in the work area 23 of the memory 22. Then, the graphic data set in the work area 23 is transferred to the communication interface 25 through the host bus 28, and transmitted to the terminal 29 through the communication line 37 by the communication interface 25.
When the graphic data is received by the communication interface 30 of the terminal 29 in step S204, the received graphic data is stored in the picture memory 32 by the control processor 31. Then, the graphic data in the picture memory 32 is stored in the frame buffer 33 by the control processor 31, and the figure is raster displayed on the CRT 34 on the basis of the graphic data stored in the frame buffer 33.
When edit data indicating correction types such as deletion and addition, and correction starting points are entered by the operator's handling of the digitizer 35 in step S205, the edit data is transferred to the communication interface 30 by the control processor 31, and transmitted to the host 21 through the communication line 37 by the communication interface 30.
When the edit data is received by the communication interface 25 of the host 21 in step S206, the host processor 26 corrects the graphic data stored in the work area 23 on the basis of the edit data. After correction, the graphic data set is transmitted to the terminal 29 through the communication line 37 by the communication interface 25 as correction display data.
When the correction data is received by the communication interface 30 of the terminal 29 in step S207, the received correction data is stored in the picture memory 32 by the control processor 31, and subsequently, the graphic data in the picture memory 32 is loaded on the frame buffer 33. Then, the drawing is displayed on the CRT 34 on the basis of the graphic data in the frame buffer 33. Then, determination is made in step S208 as to whether or not the operator manipulates the terminal 29 to transmit an end command to the host 21. If the result is negative, the processing returns to step S205, whereas if it is positive, the processing moves to step S209, where all the graphic data in the work area 23 are transferred and stored in the common file storage unit 27.
However, every time the drawing is corrected, all the graphic data in the work area 23 are sequentially transferred from the host 21 to the terminal 29 so that the corrected drawing is displayed on the CRT 34 on the basis of all the graphic data received. As a result, time period from the correction of the graphic data to the display of the corrected drawing cannot be reduced beyond a certain limit. Hence, the operator must wait patiently until the corrected drawing is displayed after correcting the graphic data. This will hinder the edit work from being smoothly carried out.
To avoid such a waiting time, it may be possible to correct data without displaying, but this will lead to misoperations by the operator.
Furthermore, another problem arises from correcting the graphic data in the work area 23 in the data correction. For example, when an error is found in the preceding correction, and hence an attempt is made to restore the graphic data before correction, it is necessary to load the uncorrected graphic data again from the common file storage unit 27 onto the work area 23. This is because only the corrected data is present in the work area 23, and not the uncorrected graphic data. Thus, the restoration takes a rather long time.
To solve such problems, the following correction method is conceived. First, the same application program as that of the host 21 is stored in the terminal 29. Second, the graphic data in the work area of the host 21 is loaded on an edit area provided in the terminal 29 in accordance with the application program before correction. Then, the graphic data loaded on the edit area is corrected. However, this presents a problem in that the cost of the entire system will increase with the number of the terminals 29 because of the cost of the hardware and software, which presents another problem that the system is not practical.